In recent months, the Canadian device maker has held talks with Baltimore-based mobile ad network Millennial Media about a potential acquisition, these people said. But the talks have stalled over disagreements regarding the value of Millennial, which serves advertisements on its own network of mobile websites. It also brokers ad sales to a group of other mobile ad networks.

Encouraged by the recent sale prices fetched by rivals AdMob and Quattro Wireless, Millennial has asked for between $400 million to $500 million, these people said. RIM has been unwilling to pay such a price, these people added.